'Now, nobody's saying the Chatsworth Estate is the Garden of Eden, but it's been a good home to me and me kids, who I'm proud of! 'Cause every single one of them reminds me a little of me. They can all think for themselves! Which they've me to thank for."

The introduction to Channel 4's iconic comedy drama Shameless, voiced each episode by lead character Frank Gallagher, has become true not just of his fictional children but also of the phenomenally successful "kids" who played them.

Like a Manchester council estate version of Rada, Shameless has become a launchpad for some of the most in-demand stars of British film and television. Anne-Marie Duff (The Virgin Queen) and James McAvoy (Atonement) graduated from the show to become a Bafta power couple, Maxine Peake impressed as Myra Hindley on ITV, Gerard Kearns won a South Bank award for his performance in the BBC's Iraq drama The Mark of Cain, and even Frank Gallagher - aka David Threlfall - has been lured to Hollywood, turning up with Cate Blanchett in Elizabeth: The Golden Age.

The latest star to graduate from the Chatsworth Estate is Rebecca Ryan, still playing Debbie Gallagher in the series, but also making her London stage debut at the Royal Court in the former Edinburgh fringe hit, Scarborough.

Ryan has grown up on Shameless: she was 11 when the first series was shown in 2004 and has had to show Debbie going through everything from her first period to her first love affair. So, when I meet the 16-year-old Mancunian in the bar of the Royal Court drinking water, it is disconcerting to realise how familiar she is: her strong accent, slight frame, dark features and aquiline face are embedded in the mind from numerous, unflinching close-ups.

"I am always shocked how much people recognise me," she says, "although it's much worse in Manchester than it is down here." Ryan fell into acting almost by accident. She was initially set on a career in Irish dance, following in the footsteps of her mother, a former world champion.

"I've been dancing since I was three," she says, "and for a long time it was all I wanted to do." Then, at the age of six, she accompanied her older brother Charlie to some auditions and got picked to appear first in a stage production of Tommy. "I had just rolled out of bed and had an Arsenal shirt on with some trackie bottoms but I was the right height," she says.

A few years later she landed a role in the TV drama State of Play and so impressed its writer, Paul Abbott, that he subsequently offered her the role of Debbie, the youngest Gallagher daughter, in his new drama Shameless. The first episode alone was a rampage of fighting, drinking, swearing and sex - hardly an ideal environment for an 11-year-old girl.

"My mum read the script and she was a bit concerned but at the same time she found it incredibly funny," says Ryan.

"But the producers reassured her that all the graphic sex was filmed on closed sets so I wouldn't get to see it." By the fourth episode Debbie was under the spotlight for stealing a baby, leading to a paedophile witch-hunt on the estate.

"Although she is nearly the youngest, Debbie acts like the head of the family," says Ryan. "She is the only sensible one and makes sure everyone is looked after. But I love that she is also quite weird - stealing children and selling porn videos. She obviously thinks she is doing the right thing." This exposure to a very adult level of moral ambiguity seems like perfect preparation for Ryan's new role in Scarborough - as a 15-year-old having an affair with her teacher.

Despite claiming to be nothing like Debbie Gallagher - "She wears terrible clothes and is really neat and tidy" - Ryan clearly shares a preternatural maturity that has given her the confidence to take on an intense two-hander in which she has to enact a sex scene a few feet from the audience.

"I want to show people that I can do different things than Debbie from Shameless," she says.

"In rehearsals I was nervous but for the performances I feel excited. I just want to go out there and enjoy it."

Ryan is endlessly enthusiastic about her "brilliant" Shameless experiences, but level-headed enough not to start counting on a future in showbiz just yet.

"Seeing Anne-Marie and James on the big screen is amazing and I've started to enjoy things like period dramas - although I would have to work on my posh accent," she says.

"But it could all end tomorrow and I would be just as happy to go back to my dancing.

Scarborough is at the Royal Court, London SW1 (020 7565 5000), until March 15